Problem 122 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I List II 1\. efflorescent (i) \(\mathrm{NaOH}\) 2\. deliquescent (ii) \(\mathrm{KOH}\) 3\. fusion mixture (iii) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{K}_{2} \mathrm{CO}_{3}\) 4\. washing soda (iv) \(\mathrm{Na}_{2} \mathrm{CO}_{3} .10 \mathrm{H}_{2} \mathrm{O}\) The correct matching is \(\begin{array}{llll}1 & 2 & 3 & 4\end{array}\) (a) (ii) (i) (iv) (iii) (b) (i) (ii) (iii) (iv) (c) (ii) (i) (iii) (iv) (d) (i) (iii) (iv) (ii)

Step-by-Step Solution

Answer

The correct matching is (b): 1 with (i), 2 with (ii), 3 with (iii), 4 with (iv).

Step 1: Understanding Efflorescent

Efflorescent substances lose water to the atmosphere and form a powdered or crystalline surface. Sodium carbonate decahydrate, \( \mathrm{Na}_{2} \mathrm{CO}_{3} .10 \mathrm{H}_{2} \mathrm{O} \), also known as washing soda, is a common example of an efflorescent compound. Thus, 1 matches with (iv).

Step 2: Understanding Deliquescent

Deliquescent substances absorb moisture from the atmosphere until they dissolve in the absorbed water. Sodium hydroxide, \( \mathrm{NaOH} \), is known to be deliquescent. Thus, 2 matches with (i).

Step 3: Understanding Fusion Mixture

Fusion mixture typically refers to a combination that can be heated to assist in the decomposition of substances without reacting with the analyte. A common fusion mixture is \( \mathrm{Na}_{2} \mathrm{CO}_{3} \) and \( \mathrm{K}_{2} \mathrm{CO}_{3} \). Thus, 3 matches with (iii).

Step 4: Understanding Washing Soda

Washing soda is sodium carbonate decahydrate, known chemically as \( \mathrm{Na}_{2} \mathrm{CO}_{3} .10 \mathrm{H}_{2} \mathrm{O} \), which was matched in Step 1 as efflorescent. However, here it's identified in the problem as washing soda, matching with (iv). Thus, 4 matches with (iv).

Step 5: Verify the Matching Order

Based on the matchings: 1 with (iv), 2 with (i), 3 with (iii), 4 with (iv). The closest option that follows this order per List II is option (b): (i), (ii), (iii), (iv).

Key Concepts

Efflorescent Substances

Efflorescent substances are fascinating in the way they interact with the environment. These are compounds that have a tendency to lose water to the atmosphere. When they lose their water of hydration, they transform into a powdery or crystalline form. This transition occurs because these substances naturally contain water molecules within their crystalline structure. When exposed to dry air, the water molecules evaporate, leaving behind a dry residue.

One of the most common examples of an efflorescent substance is sodium carbonate decahydrate, also known as washing soda. As highlighted in the original exercise, this compound (\( \mathrm{Na}_{2} \mathrm{CO}_{3} .10 \mathrm{H}_{2} \mathrm{O} \)) loses its water when exposed to air, showcasing the characteristic behavior of efflorescent materials.

In practical terms, efflorescence can often be observed on surfaces like concrete or brick, where salts accumulate after water evaporates, leaving a white, powdery deposit.

Deliquescent Substances

Deliquescent substances have an opposite interaction with moisture compared to their efflorescent counterparts. Instead of losing water, they absorb moisture from the surrounding environment. This absorption is so intense that these substances can eventually dissolve in the collected water. This property makes deliquescent substances quite useful in various industrial and chemical processes where moisture control is crucial.

Sodium hydroxide (\(\mathrm{NaOH}\)) is a classic example of a deliquescent compound. When left open in air, it draws in water so efficiently that it can turn into a liquid solution over time. This property is utilized in many applications like absorbing gases and maintaining dry conditions in certain processes. Some common deliquescent substances include:

• Potassium hydroxide (\(\mathrm{KOH}\))
• Calcium chloride (\(\mathrm{CaCl}_2\))

Fusion Mixture

The term "fusion mixture" refers to a specific combination of materials used in analytical chemistry. This mixture is primarily composed of salts that can be heated to high temperatures without reacting with the substance being analyzed. The chief goal of using a fusion mixture is to help the decomposition and sometimes the solubilization of a sample to make it suitable for further analysis.

A common example of a fusion mixture includes sodium carbonate (\(\mathrm{Na}_{2} \mathrm{CO}_{3}\)) combined with potassium carbonate (\(\mathrm{K}_{2} \mathrm{CO}_{3}\)). This combination is particularly effective for some mineral extractions and material analysis procedures. By heating the sample within this mixture, it facilitates the breakdown of the sample bonds without any interference, thus providing a clearer path for examination.

Washing Soda

Washing soda, chemically known as sodium carbonate decahydrate (\(\mathrm{Na}_{2} \mathrm{CO}_{3} .10 \mathrm{H}_{2} \mathrm{O}\)), serves several important roles in households and industries. Its ability to soften water makes it an integral component in laundry detergents. It works by removing calcium and magnesium ions, which are typically responsible for the hardness of water. When washing soda is used in cleaning agents, it enhances the cleaning action of detergents.

As mentioned in the original exercise, washing soda is also a prime example of an efflorescent substance. Over time, when exposed to air, it can lose its water of crystallization, demonstrating its dual functionality both as efflorescent material and a cleaning agent. Here are some other uses of washing soda:

• Degreasing kitchen utensils
• Maintaining pH balance in pools
• As a food additive and preservative